I don't know why the results are inconsistent, but Outlook doesn't recognise @media queries and will execute everything that it comes across. To stop Outlook from rendering the mobile version, one often must wrap those segments in conditional statements.
<!--[if (gte mso 9)|IE]>
everything between is in comment and executable only by the conditional - only Outlook 2000 or newer as well as Internet Explorer will execute this
wraps with the conditional but doesn't exclude the code from others - this will be executed by everything (subject to @media queries, of course) except Outlook
Not knowing what the desktop version was supposed to render, another possible explanation is that the email is being viewed where Windows has been set to zoom text. Windows converts the fonts to points, rather than pixels, and then enlarges them. Outlook does not handle that well at all and with the newly appointed point-sized fonts colliding with the pixel-sized images, tables are often broken. This XML coding will fix that:
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:v="urn:schemas-microsoft-com:vml">
<!--[if gte mso 9]>
I hope that helps, Kim.
I agree entirely with Mark Robbins. I don't know how they expect to deliver the correct version to each individual recipient.
I wonder if they're confusing terms. Perhaps they're thinking that responsive is mere scaling and don't understand that true responsive design changes (stacking, alternate images, etc.) are accomplished in the same HTML file.